A door position restraining apparatus for restraining a position of an opened door in a door apparatus for a vehicle provided with a hinge is disclosed in JP2009-235844A, hereinafter referred to as Reference 1. Reference 1 discloses an apparatus using an opening-closing movement of a door to switch a state of the apparatus between a movement restraining mode and a movement allowing mode without using an actuator. More specifically, the apparatus includes a movement restraining mechanism that switches the state of the restraining mechanism to the movement restraining mode in response to rotation of a change ring rotating in a first direction by an operation where movement of opening the door is stopped at an intermediate position followed by moving the door slightly in a closing direction. Furthermore, in a state where the door is moved in a direction to fully close the door, the change ring is driven in a second direction in response to the door closing operation so that the movement restraining mechanism switches to the movement allowing mode. In other words, the apparatus disclosed in Reference 1 switches the state of the apparatus between the movement restraining mode and the movement allowing mode without using an actuator by making use of a manually operated door closing operation.
In JP2010-95855A, hereinafter referred to as Reference 2, a door opening-closing retaining apparatus that retains a door at a selected opening degree is disclosed. Reference 2 discloses an apparatus to improve door opening-closing operation performance by providing simple and comfortable operation by restraining a check force from being exerted while opening and closing the door. More specifically, during a period during which the door is operated to open, an engagement release operation member is operated to disengage a checking mechanism so that the door is smoothly opened in a state where the check force is not exerted. During a period during which the door is operated to close, closing operation of the door disengages the checking mechanism. In other words, without an independent procedure to operate the engagement release operation member, the door may be closed.
Furthermore, an automatic opening-closing apparatus for a vehicle for an application of a power back door, which is a back door for a vehicle provided with a drive source, is disclosed in JP2006-265982A, hereinafter referred to as Reference 3. Reference 3 discloses an apparatus to improve opening-closing operation performance of an opening-closing body in a manual operation by allowing the opening-closing body to be manually operated to open, to close and to stay still in an intermediate position by an operation at a single operation portion. More specifically, the automatic opening-closing apparatus for a vehicle is described as an apparatus for automatically opening and closing the opening-closing body mounted on a vehicle body in a state where the opening-closing body freely makes opening and closing movements in upward-downward direction via a hinge. The automatic opening-closing apparatus for a vehicle includes a drive source for driving the opening-closing body to open and to close, an opening-closing operation portion, which is operated by an operator, arranged on the opening-closing body, an auxiliary opening force generating means arranged between the vehicle body and the opening-closing body and biasing the opening-closing body in an opening direction, and a clutch arranged between the opening-closing body and the drive source and selectively connecting a power transmission path between the opening-closing body and the drive source by an operation of the opening-closing operation portion. In a state where the clutch is in a disconnected state, even in a case where the opening-closing operation portion is operated, the automatic opening-closing apparatus for a vehicle maintains the clutch in a disconnected state during a period during which the opening-closing body is within a range within which the opening-closing body is recognized as closed and during a period during which the opening-closing body is within a range within which the opening-closing body is recognized as open. Note that, the range within which the opening-closing body is recognized as closed is a range where the opening-closing body is at a position between fully closed position and a position where the opening-closing body is half-latched. The range within which the opening-closing body is recognized as open is a range where the opening-closing body is at a position between fully opened position and a predetermined position.
In addition, a door retaining control apparatus for a sliding door of a vehicle for an application of a power sliding door for a vehicle is disclosed in JP3816511B, hereinafter referred to as Reference 4. Reference 4 discloses an apparatus to retain a sliding door with a transmitted retaining force that is appropriate for manually operating the sliding door to open and close while retaining the sliding door immovable by self-weight under any condition. More specifically, the door retaining control apparatus for a sliding door of a vehicle includes a sliding door to be moved by a sliding door moving mechanism and moved on a guide track arranged on a vehicle to open and close the sliding door, a clutch mechanism selectively transmitting power from a drive source to the sliding door moving mechanism, a movement detection means detecting movement of the sliding door, and a clutch control means adjusting the transmitted retaining force at the clutch mechanism. The clutch control means adjusts the transmitted retaining force to restrain movement of the sliding door when the clutch control means receives an output from the movement detection means and detects that the sliding door has further moved in a direction toward opening the sliding door from a fully opened position or from a position close to the fully opened position. Then, after a predetermined time has elapsed, the clutch control means adjusts the transmitted retaining force to minimum, which is a smallest force required for retaining the sliding door in a non-moving state.
Furthermore, a drive system for opening and closing, for example, a tail gate or a trunk of a vehicle is disclosed in WO2009059747A, hereinafter referred to as Reference 5. Reference 5 discloses an apparatus including a connecting apparatus connected to an electric motor in a driving side and to a closing member in an output side. The connecting apparatus includes a first friction engagement element providing pushing pressure on a contact surface of a non-moving member and a second friction engagement element connecting a driving element to the driven element and configured to provide pushing pressure on a contact surface of a transmission element. In a state where the drive system is driven by an electric motor, the second friction engagement element transmits torque, which is generated in the driving side, from the driving element to the driven element. In a state where the closing member of the drive system is manually operated, the transmission element transmits torque generated in the driven side to the first friction engagement element so that restraint on the contact surface is released. Note that, from drawings in Reference 5, the closing member is a tailgate, or a back door, and the friction engagement elements are coil springs.
The door position restraining apparatus disclosed in Reference 1 requires an operation where movement of opening the door is stopped at an intermediate position followed by moving the door slightly in the closing direction in order to bring the door position restraining apparatus to the movement restraining mode. In addition, an operation to move the door in the closing direction is required to switch the door position restraining apparatus from the movement restraining mode to the movement allowing mode. Furthermore, the door position restraining apparatus disclosed in Reference 1 is not allowed to operate the door in the opening direction from the state in which the door position restraining apparatus is in the movement restraining mode. Accordingly, an operation performance of the apparatus disclosed in Reference 1 leaves room for improvement. Furthermore, the door opening-closing retaining apparatus disclosed in Reference 2 requires an operation of the engagement release operation member to release the door from a retained state. Accordingly, an operation performance of the apparatus disclosed in Reference 2 leaves room for improvement. In a case where a rotational member in the apparatus disclosed in Reference 1 or in Reference 2 is a door and a retaining member in the apparatus disclosed in Reference 1 or in Reference 2 is a vehicle body member, a switching mechanism is required to smoothly switch between an operation allowed state, which is a state where movement of the rotational member is allowed, and a movement restrained state, which is a state where the movement of the rotational member is retained at a selected stopped position, with a simple operation and to reliably retain the movement restrained state.
Each of the apparatuses disclosed in Reference 3 through 5 uses an electric motor as a drive source and furthermore requires a clutch mechanism. A clutch mechanism, in general, is defined as a mechanism that selectively transmits power from an engine body to a driven body, which is a mechanism that manually or automatically connects and disconnects between the engine body and the driven body to engage and disengage the engine body and the driven body. The clutch mechanism is mainly divided into two types, which are a positive clutch that engages by engaging teeth and a friction clutch that engages by friction. In each type, the clutch mechanism engages to transmit power from the engine body to the driven body and disengages to stop transmitting power. The friction clutch transmits rotation by frictional resistance, or frictional force. Accordingly retaining a frictional state while transmitting power is considered important. In a state where the power is not transmitted, the friction clutch is in a disengaged state. A separate consideration is required for retaining the friction clutch in the disengaged state, which is a state in which the operation of the friction clutch is stopped.
Particularly in each of References 3 and 4, an electromagnetic type clutch is used as a clutch mechanism. Accordingly, an electrical control is required to retain the clutch in a state in which the operation of the friction clutch is stopped. In addition, in each of References 3 and 4, a worm reducer, which is low in efficiency, is used. Accordingly, a large output type electric motor is required and the apparatus becomes large in size, heavy in weight, high in cost, and large in power consumption. In comparison, a size of an electric motor may be reduced in the system disclosed in Reference 5. Nevertheless, the system in Reference 5 is configured to increase a retaining force for retaining a tailgate. Power required for operation during manual operation of the tailgate has increased as much as the retaining force increased to retain the tailgate. Accordingly, a manual operation performance is decreased. In a state where the system is driven by a motor, sliding movement of coil springs results in resistive loss, which leads to a difficulty in reducing size and reducing power consumption.
A need thus exists for a switching mechanism, which is not susceptible to the drawbacks mentioned above.